In multilayer semiconductor devices, excess topology or non-planarity is often introduced during fabrication by underlying partial structures, particularly levels of metal, such as metal lines or buses. Insulator layers over the underlying structures generally conform to the topology and introduce the same non-planarity. A result is that stress is introduced onto the device and crevices resulting from the non-planarity collect unwanted particles, both of which are causes for device degradation, such as, for example, short circuits and a concomitant reduction in ultimate yield. This non-planarity also causes a loss in metal interconnect linewidth control.
In the prior art, non-planarity problems are alleviated by a procedure known as resist etch back wherein a resist or other conformal material is spun over the non-planar layer having a thickness greater than the highest peak of the non-planar layer with a resulting planar or flat resist surface, regardless of the topology. The resist is then etched back with an etchant which etches the non-planar layer at the same etch rate as the resist until all of the resist has been removed and the former non-planar layer has been planarized.